1. Field of the Invention
The invention relates to a method and apparatus for determining whether or not the flow rate through one or more orifices in a workpiece are within permissible tolerance when compared to the flow rate through one or more matching orifices in a master part. This determination is based upon characteristics of fluid flow passing through the orifices in the workpiece and in the master part. Additionally, the subject invention is directed to a method and apparatus for machining the one or more orifices in a workpiece so that the geometry better conforms to the geometry of the matching one or more orifices of the master part. Finally, the invention relates to a method of determining the flow rate through the one or more orifices of the workpiece.
2. Description of Related Art
Components such as fuel injectors and orifice plates typically include small orifices with flow rates that must be precisely controlled to very small tolerances. Manufacturers of such components generally make use of a measurement device, such as a flow bench, which forces a calibration fluid through the component orifices at a precise pressure and then measures the flow rate through the component orifices. This flow measurement may be made by a flow meter based on a wide range of technologies, including Coriolis meters, positive displacement meters such as gear and piston pumps, turbine meters, and vortex shedding flow meters.
FIG. 1 is prior art and shows a schematic of a typical flow bench 300 used for measuring the flow rate through a workpiece 310 having one or more orifices (not shown) extending therein. Calibration fluid from a reservoir 315 is forced by a pump 325 past a heat exchanger 330 and a filter 335 and then forced under pressure through at least one orifice (not shown) in the workpiece 310. The flow rate downstream of the workpiece 310 is measured directly by a flow meter 340. There must be a minimum amount of downstream pressure of the fluid past the workpiece 310 to drive the fluid through the flow meter 340. Upon exiting the flow meter 340, the fluid is re-introduced into the reservoir 315.
However, methods using flow meters often create bottlenecks in the overall manufacturing process due to lengthy measurement times. Since the usual measurement method is to measure the flow rate through a part at a given pressure, then depending on the means of supplying pressurized calibration fluid to the part, it may take several seconds to achieve a desired pressure and then to stabilize the fluid flow at that pressure, at which time flow measurements may be taken. Moreover, the flow measurement devices often require long measurement times to deliver a stable measurement. As a result, using conventional techniques, measurement times of 25 to 60 seconds or more are often required to determine whether or not a part is within a prescribed flow tolerance range.
Use of a conventional flow bench gives the operator an absolute value for the flow rate, whether it be mass flow rate or volume flow rate, through a part at the measurement pressure. If the flow rate is within tolerance, the part passes. If the flow rate is below the target, the part may be sent back for rework. If rework is not possible, the part would be scrapped. If the flow rate through the part is too high, the part is usually treated as scrap.
There is a need to produce a gauge similar to a go/no-go gauge used for thread, hole and other machining operations for use in checking the flow rate through an orifice. Such a gauge would simply indicate whether a part was in tolerance or, if out of tolerance, indicate the direction in which the discrepancy occurred. Such a determination would be possible without having to produce a numerical value of the flow rate. Because an actual value of the flow rate is not required, it would be possible to employ faster techniques.